A former security guard who developed post traumatic stress disorder (PTSD) working at Manus Island detention centre is locked in a fight with Wilson Security and the Australian Immigration Department after his insurance claim was rejected.

Ricky Morse, 54, says he has been suffering from symptoms, including paranoia, ever since he left the troubled Papua New Guinea (PNG) detention centre two years ago.

Mr Morse said he lodged an insurance claim with Wilson Security's insurer Southern Cross Assurance Limited, based in Port Moresby.

But the insurer rejected his claim, arguing Mr Morse had a pre-existing condition.

In a letter to Mr Morse, Southern Cross Assurance said his mental illness "did not commence during the period of employment but prior to it, and also he was aware of the illness but failed to disclose it".

But Mr Morse said he and his psychiatrist both disagreed with the company's assessment.

"Because I've had PTSD before they classed it as a pre-existing injury — I'm ex-military, I'm ex-copper, so I've had mental issues. Then I had the incident which caused me to relapse.

"When I went to see my psychiatrist, he said 'no, it's not a relapse, it's a new injury caused by the incident over there'.

"It's like breaking your leg, you break it, it heals — you break your leg again it's another injury. So that's what he said.

"That's why the claim ... it's been denied."

Mr Morse said it had taken a heavy toll on him and his family.

"I just want to get well and I can't get well until this fight is over," he said.

"At the end of the day, we've got people on an Australian contract, an Australian company with a contract with a PNG company that is not registered to Australia and we have no appeal."

The ABC has spoken to other former security guards who worked with Mr Morse and they said he had been treated disgracefully by Wilson Security.

"Trying to talk to Wilson's and garner some support from hierarchy was always hard, especially when you were looking at something like a PTSD claim," one former worker said.

"They pretty much just shut the door on you, so it's very difficult to communicate with Wilson's about issues you do have."

'It's very unfair'

Former security guards want the company to treat its former employees fairly and provide support.

"Talk to [the workers] would be the first thing and see what their issues are, and then work together to reach an agreement or something that helps everyone move forward," one former worker said.

"Whether that's retraining and or employment in Australia.

"All the people that I worked with over there were fantastic guys, they were wonderful security guards, and they did take pride in their work and they're all great people — they all need to be looked after."

Alison Barrett from law firm Maurice Blackburn said it had been involved in a number of other cases where workers had been injured on Manus Island.

She said many of those workers also had their insurance claims rejected.

"It's very unfair and quite often the enquiries we're talking to — all they want is some money to reimburse them for their time off work, to pay for their much-needed medical treatment," she said.

"Being unable to access financial assistance ... prolongs their injury and their rehabilitation, makes it very difficult for them to get back to work and then puts a lot of pressure on their families."

Ms Barrett said Wilson Security needed to take responsibility for the situation.

"All Australian workers should be entitled to coverage for workers compensation and what we've seen is Wilson has gone through a process of finger-pointing and blame-shifting," she said.

Wilson Security referred the ABC to the Immigration Department when it was contacted for comment.

The Immigration Department said service providers were responsible for ensuring any sub-contractor complied with strict clauses on insurance cover.

It said support provided to staff employed by sub-contractors was a matter for those organisations.

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